A liquid crystal display (LCD) is a non-self emitting display, i.e. it needs a self-emitting device to serve as a light source. Such a light source is generally called a backlight module. There are usually two types of backlight modules: a direct-light type and an edge-light type. A direct-light type backlight module conventionally includes components such as cold cathode tubes that serve as the light sources, a diffuser, a prism sheet, etc. In order to evenly distribute light emitted from the light sources and provide a desired illumination field for an LCD, a deliberated control of the spaces/pitches between the light sources, the distance between the light sources and the diffuser, and distance between the light sources and the prism sheet is needed. However, due to the optical complexity in a backlight module, it is usually difficult to create a uniform illumination in LCDs. In addition to the aforementioned components in the direct-light type backlight module, an edge-light type backlight module further includes a light guide plate for guiding and/or diffusing light from the light sources. Nevertheless, the difficulty to create a uniform illumination still exists in the edge light type backlight module. Besides, the components forming the aforementioned two types of backlight modules are too complicated and therefore constitute an obstacle to reducing the production cost.
In order to overcome the aforementioned problems, U.S. Pat. No. 6,598,998 discloses a side light-emitting diode (LED) including an LED and a lens directing light from the LED to the side of the lens, i.e., to the direction substantially perpendicular to that of light emitted from the LED. The lens includes a sawtooth portion and a funnel-shaped portion for redirecting the light. However, the two portions are too large in scale and thereby increase the total thickness of the lens. Furthermore, such a lens needs to be mounted to each LED. Therefore the processing complexity and production cost for manufacturing LEDs are increased, and the light extraction efficiency of such a side LED is reduced to a certain extent, usually more than 10%.
U.S. Pat. No. 6,582,103 discloses a light source apparatus including a cavity having reflective surfaces and an output area, wherein at least one light source is disposed in the cavity, the light source comprising a point source and an optical diverter. The optical diverter is used to redirect the light emitted from the point source laterally or downwardly to the cavity having the reflective surfaces, thereby increases brightness and light-mixing performance. A diffuser is located within or over the output area. Despite the '103 patent may avoid the non-uniform illumination occurred in the backlight modules, an optical diverter is needed to mount to each light source, so that the overall packaging process is complicated and costly. Moreover, since each point source is in operation with a corresponding independent optical diverter, a light spot is apt to be formed. Thus, the thickness of the backlight module has be increased for enhancing the light-mixing performance, but the brightness decreases with the increase of the distances between the light sources, so that the spatial arrangement of the light sources has to be deliberately controlled in order to maintain the illumination uniformity of the backlight module.
The aforementioned patent arts are characterized in common by adding a lens or a light-guiding device to each point source, and may cause five problems: (1) complicated process; (2) high packaging cost; (3) increased backlight module thickness; (4) uneasily-controlled illumination uniformity of the entire backlight module; and (5) poor light extraction efficiency.